Gallien-Krueger 250ML Distortion Preamp

[Blackboarcult]

By request.
For those who don't know this gadget, it was a lunchbox amp made famous in the late 80s by Iron Maiden and Rush.

Haven't had a chance to build it yet, but it behave rather nice on my breadboard. I tried to implement a gain pot, but my lack of knowledge gave mediocre results, plus the circuit is already well balanced and both gain options sound almost perfect.

You'll need a bipolar voltage converter (geez, it's becoming a bad habit in my layouts recently...)

Tonestack is not included, I'm working on a separate board for it.

Enjoy!

[ibanez48]

I read were you said getting the distortion to sound good. Is there a certain way you have to adjust the trimmers.

[Blackboarcult]

I started with trimmers in the middle position (factory setting, methinks) and adjusted til I found a good sounding spot, which was almost full-on for maximum gain  a matter of taste really... as I only had multiturn pots to test it, hard to say which way heheh

[ibanez48]

Ok thanks hopefully I can build it in a couple of days. I’ll let u know how it turns out.

[ibanez48]

Did you ever get a separate board for the tone stack.

[Blackboarcult]

Yes, I did make a layout for the ToneStack, but coupled with a Durham Sex Drive in front and a Baja Reactor upstream to act as a "power amp simulator" or sort of... Works rather well though.
I'll try to find some time to draw it as a standalone this week.  Did you already build the preamp board?

[ibanez48]

I’m working on it now haven’t finished it yet.

[ibanez48]

I know this is a little old did u ever draw a layout for the tone stack.